The present invention relates to a membrane for concentrating amino acids and, more particularly, to a membrane for concentrating amino acids by causing amino acids to permeate against the concentration gradient and to a process for concentrating amino acids by using the membrane for concentrating amino acids.
Heretofore, such hydrophilic polymeric membranes as cellophane (cellulose), collagen, keratin, and polyvinyl alcohol have been known as the membranes which are permeable to amino acids dissolved in an aqueous solution. These membranes permit amino acids to permeate along the direction of concentration gradient, or from the high concentration to the low concentration, because permeation is the passing of amino acids through the gell structure of the polymer constituting the membrane. Thus, they have no function to permit amino acids to permeate against the concentration gradient, or from the low concentration to high concentration, whereby to concentrate amino acid solutions.
The present inventor has previously proposed a polyvinyl chloride membrane containing a metal chelating agent, said membrane permitting metal ions or lipophilic anions to permeate against the concentration gradient, whereby concentrating the ions. To concentrate metal ions in a solution by using this membrane, the solution is separated by this membrane and lipophilic anions are added to one portion of the solution. Metal ions in one moiety of the solution diffuse into the other moiety across the membrane, resulting in concentration of metal ions. In the similar manner, lipophilic anions are concentrated by dividing the solution containing lipophilic anions with the membrane and adding metal ions to one moiety of the solution. The polyvinyl chloride membrane containing a metal chelating agent is able to concentrate ions. In other words, when such a membrane is placed in a solution to divide it into two, the membrane causes specific metal ions to diffuse across it from one side of the solution to the other. It should be noted that concentration by this method is applicable to metal ions and lipophilic anions, but not to hydrophilic substances of large molecules like amino acids.